High molecular weight linear polyesters and copolyesters are well known and have enjoyed continued and increasing commercial success. These are especially useful resins because they provide compositions with excellent moldability, and molded articles therefrom having smooth and glossy surface appearance, high strength, stiffness temperature resistance and other desirable properties.
Additionally, these resins may be modified to improve certain physical properties and further broaden their scope of application by incorporating therein various additives including fillers and reinforcing agents to enhance toughness and vary the stiffness of the material.
Blends of such polyester resins with one or more second resins have become of significant commercial interest because such second resins, carefully selected, can greatly improve impact strength, as well as tensile strength, modulus and distortion temperature under load in parts molded from such compositions. By way of illustration, such second resins can compromise minor proportions of aromatic polycarbonate resins, as described for example, in Kawase et al, U.S. Pat. No. 3,953,539.
There is a tendency, in such polyester-polycarbonate blends, for there to be an undesirable transesterification reaction between the polyester resin and the polycarbonate resin. This chemical reaction is manifested by there being a yellowing of the resulting blended resin.
Therefore, there is a need in the art for a method of preventing or substantially hindering the transesterification reaction between polycarbonates and polyesters in mixed blends of said resins.
It has now been discovered that certain phosphate fibers, specifically metaphosphate fibers, have demonstrated the ability to inhibit the transesterification reaction between polyester resins and polycarbonate resins.